1. Field of the Invention
The invention relates to the field of Web services and, more particularly, to invoking Web services using a pattern-based approach.
2. Description of the Related Art
Web services, also referred to as application services, are services that are made available from Web servers for Web users or other Web-connected applications. Providers of Web services generally are known as application service providers. Web services can range from such major services as storage management and customer relationship management to much more limited services such as the furnishing of a stock quote or the checking of bids for an auction item. Other examples of Web services can include, but are not limited to, services that provide a telephone number in response to a provided name and services that return one or more electronic mail addresses for a provided name.
Web services typically are request response based and follow the client/server model. That is, a request from a client is sent to a server for fulfillment. Typically, the request is provided to the server and is formatted according to Remote Procedure Call (RPC) protocol. In general, RPC enables one application, the client, to request a service from another application, the server. RPC allows the client, operating in one computer system, to issue the request to the server, operating in a different computer system within a network. The client application, need not have an understanding of the operational details of the network to make a request of the server application when using RPC.
The request can be sent using Simple Object Access Protocol. In other words, a SOAP message containing RPC information is sent to the server. The server can then process the received request and provide a response to the client. SOAP is a protocol that enables a program running in one kind of operating system to communicate with a program in the same or another kind of an operating system, and also computer system, by using the Hypertext Transfer Protocol (HTTP) and Extensible Markup Language (XML) as mechanisms for information exchange. SOAP specifies how to encode an HTTP header and an XML file so that a program in one computer can call a program in another computer as well as pass information.
Presently, the Web service paradigm specifies a procedure in which a request pertains to a single Web service. More particularly, each request initiates a single Web service and, therefore, is directed to a particular service provider. As such, to perform more complex actions involving more than one Web service, the client must issue a series of requests where each request is sent to a different Web service. That is, each constituent task of an action must be submitted to an appropriate Web service as a request.
If the tasks constituting the action are hierarchical in nature, such that one Web service requires information from another Web service to function, the requests must be issued to each Web service in proper order. In such cases, the client must receive a response from a given Web service so that the retrieved information can be used to build the request to be submitted to the next Web service in the hierarchy of Web services constituting the action to be performed.